SUB-KINGDOM (TYPE) III.ECHINODEEMATA. 



SIMPLE marine organisms, which are mostly bilaterally sym- 

 metrical when young, but which in the adult condition have 

 this bilateral symmetry more or less extensively masked by 

 a radial (usually pentamerous) arrangement of their parts. 

 An alimentary canal, with or without a distinct anus, separ- 

 ate from the proper body-cavity. A system of water-vessels, 

 often communicating directly with the exterior, and generally 

 connected with protrusible tubes (" feet "), is present. The 

 nervous system is radiate, consisting of an cesophageal ring 

 and radiating branches. The integument is characteristi- 

 cally hardened by the deposition in it of carbonate of lime 

 in the form of plates, granules, or spicules. 



ORDER I. ECHINOIDEA (Sea-Urchins). 

 Sub-ord. 1. Eegularia (Desmosticha). 



Fain. a. Cidaridse. Cidaris, Porocidaris. 



Fam. &. Arbaciadse. Arbacia, CwlopleuriLS. 



Fam. c. Diadem atidse. Diadema, Aspidodiadema, 



Hemicidaris. 



Fam. d. Saleniadse. Salenia. 

 Fam. e. Temnopleuridse. Temnechinus. 

 Fam. /. Echinidse. Echinus. 

 Fam. g. Echinothuridse. Asthcnosoma, Phwmosoma, 



Echinothuria. 



Sub-ord. 2. *Perischoechimdse. 



Fam. a. *Archseocidaridse. Arckceocidaris. 

 Fain. b. *Palsechinidpe. Palcechinus. 



